• Departments of Epidemiology.
• Biostatistics, Indiana University Richard M Fairbanks School of Public Health, Indianapolis, IN.

BACKGROUND: Vitamin K inhibits prostate cancer cells, and an altered expression of vitamin K-dependent proteins in prostate tumors has been linked to their aggressiveness and progression. However, little is known about the effect of vitamin K intake on prostate cancer in human populations.

OBJECTIVES: We evaluated the associations of dietary intake of phylloquinone (vitamin K-1), menaquinones (vitamin K-2), and total vitamin K with the development of prostate cancer among participants in the Prostate, Lung, Colorectal, and Ovarian Cancer (PLCO) Screening Trial.

DESIGN: Dietary intake of vitamin K was assessed with the Dietary Questionnaire (DQX) at baseline and the Dietary History Questionnaire (DHQ) at the third anniversary of randomization by using high-performance liquid chromatography-based food-composition data obtained from the USDA and published studies. During a median follow-up of 11.8 y, 2978 cases of prostate cancer (including 490 advanced cases) were identified from the 28,356 men who completed DQX. Similarly, 2973 cases of prostate cancer (including 647 advanced cases) were documented from the 48,090 men who completed DHQ. Cox proportional hazards regression was used to estimate prostate cancer risk in relation to the dietary intake of vitamin K.

RESULTS: After adjustment for confounders, dietary intakes of phylloquinone, menaquinones, and total vitamin K, assessed with either the DQX or DHQ, were not significantly associated with the risk of advanced, nonadvanced, and total prostate cancer. These results remained virtually the same when vitamin K intake was modeled as a categorical (divided into quintiles) or continuous (per IQR increase) variable or after outliers of total vitamin K intake (defined as a value that falls above the sum of third quartile and twice the IQR) were excluded.

CONCLUSIONS: The present study does not suggest that vitamin K intake influences the occurrence of total and advanced prostate cancer in the general US population.